The present invention relates to a method for implementing Wind Energy Converting Systems (WECS in the following) fitted with anti-icing systems, in accordance with the installation sites where they are meant to operate for producing mechanical work or electric energy.
The present invention also relates to means for implementing said method, to rotor blades fitted with said means, and to a computer program product which can be loaded in the memory of at least one computer and which comprises portions of a computer program for executing at least a portion of said method.
The aforesaid method is particularly suited to being applied to WECS provided with an anti-icing system, as described in the international patent application WO 2004/036038, being equivalent to the Italian patent application No. TO 2002A000908 in the name of the same Applicant of the present application.
For the sake of brevity, the contents of said international and Italian applications are intended to be incorporated in the present description, and the published document should be referred to for further details.
It is however opportune to specify that, in the following description and in the appended claims, the term “anti-icing system” indicates any system that generates a so-called “de-icing” and/or “anti-icing” effect on the surface of a wind rotor blade through effusion of a fluid flow inside the blade itself.
This fluid flow runs through a plurality of holes obtained on at least a portion of the blade surface, which holes are so shaped, numerous, and have such a surface density as to create a fluid cushion, in particular an air cushion effusing from the blade and being adapted to interact with the fluid flow which impacts upon the blade surface.
The “anti-icing” effect has the purpose of preventing ice from forming and growing on the blade surface, whereas the “de-icing” effect is used for removing ice already formed on the blade.
Anti-icing devices may be a key factor for the economic tenability of WECS, in particular when they are installed on sites having unfavourable climates, i.e. where icing occurrences on the blades are high, for example sites where there is air at high degree of humidity and temperatures near to 0° C.
Icing occurrence on wind turbines blades depends on many factors, defined by those skilled in the art as “problem variables”, the most important ones being: site or environmental variables, machine variables, and mixed variables.
Site or environmental variables can be subdivided into:                climatic variables, such as typical wind speed on the installation site, ambient pressure and temperature, and        weather variables, such as relative humidity, water content per volume unit, and mean diameter related to drops forming a cloud in proximity to wind turbine.        
Machine variables are typically the temperature of the outer surfaces of the machine while operating and in idle conditions, the geometric parameters of the blade, and the functional parameters of the WECS, among which rated power and power reserved for the anti-icing system.
Mixed variables are those variables which derive from the interaction between the machine and the site, such as, for example, the coefficients of the external thermal exchange occurring on the outer surfaces of the WECS, water pick-up efficiency and water collection efficiency on the same surfaces.
Site or environmental variables depend only on the typology of the site where the WECS is installed.
Machine variables determine geometrical characteristics, such as typologies and parameters of blade and rotor profiles, as well as functional characteristics, such as revolution speed, rated power, power control and management protocols.
Mixed variables depend on both site parameters and machine parameters: the most important ones are the Reynolds number, the characteristics of the anti-icing system, and the generation and control of the thermal power to be supplied to the system. As a matter of facts, the high number of variables involved makes it very difficult to design and manufacture a WECS fitted with a “de-icing” and/or “anti-icing” system, independently of the specific anti-icing and/or de-icing system as applied.
The design and calculation complexity of models simulating the operating conditions of a WECS mostly emerges when calculating the installed power, the absorbed energy and the control of the anti-icing system, the aspects thereof typically lead to poor efficiency of the adopted solutions. This is due to the fact that icing occurs on the rotor blades differently according to changes in weather conditions and in the revolution speeds of the WECS rotor, or to changes in the power control strategy of the system in terms of active control, e.g. the active or passive stall of the various profiles of the blade.
An objective design problem is to determine, in a reliable manner, the power of the anti-icing system to be installed and those regions of the blade surface where said power is to be made available, which regions are very difficult to identify. As a matter of facts, experience has shown that power calculations obtained with known systems are not enough reliable and lead to considerable inefficiency.
The above described problems represent a clear limit in dimensioning anti-icing and de-icing systems as to their capacity to adapt to different installation sites of the WECS, i.e. to different weather and operating conditions of the WECS. As far as the applicant knows, the prior art does not provide any known method for implementing a WECS fitted with an anti-icing and de-icing system in accordance with the specific environmental conditions of the site where it is intended to operate.
In practice, a WECS is engineered by sizing the anti-icing system according to general empirical parameters. For example, when designing the anti-icing and de-icing system, it is customary to perform a general empirical calculation in order to calculate the thermal power to be subtracted from the generator and supplied to the anti-icing and de-icing system. Such power is typically determined based on the experience of the WECS' supplier, without actually checking any further.
No verification is therefore made before a WECS fitted with an anti-icing and de-icing system is installed, so that its efficiency is evaluated only during its normal operation, i.e. after designing, delivery, and the completed on-site installation of the WECS.
It is also known that companies specialized in WECS designing seldom manufacture rotors and rotor blades themselves, which are calculated and sized according to standard construction and aerodynamic parameters. The anti-icing and de-icing system, when used, is generally installed after blades manufacturing; only in rare cases it is installed in parallel with the blades construction.
For example, there are conventional anti-icing and de-icing systems based on the use of electric resistances associated with a portion of the outer surfaces of the rotor blades, which are applied to the outermost blade layer only in a limited region, such as the one across the leading edge, typically for a variable length; this solution provides a low-efficiency of the system.